Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.50	12.839%	$95.349	$95.35	$95.35	$95.30
Purchase #2	$214.32	8.768%	$233.1116	$233.11	$233.10	$233.10
Purchase #3	$151.51	11.156%	$168.4125	$168.41	$168.40	$168.40
Purchase #4	$34.62	6.576%	$36.8966	$36.90	$36.90	$36.90
Purchase #5	$83.81	7.758%	$90.312	$90.31	$90.30	$90.30
Purchase #6	$10.51	9.772%	$11.537	$11.54	$11.55	$11.50
Purchase #7	$244.55	12.176%	$274.3264	$274.33	$274.35	$274.30
7 purchase totals =	$823.82		$909.9451	$909.95	$909.95	$909.80